The overall objective of this project is to evaluate recombinant interferon gamma as adjuvant therapy in the treatment of diseases caused by intracellular microorganisms. Specifically, we will determine if the combination of interferon gamma and standard chemotherapy will accelerate healing in patients with lepromatous leprosy and tegumentary leishmaniasis. Functional and phenotypic studies of peripheral blood and intralesional mononuclear cells before and after therapy will characterize the immunopathology and be correlated with clinical responses. The specific aims are as follows: 1) To investigate the efficacy and safety of the combination of interferon gamma and antimony therapy in the treatment of diffuse cutaneous leishmaniasis. 2) To evaluate the adjuvant effect of interferon gamma and low-dose antimony therapy in the treatment of cutaneous leishmaniasis and development of mucosal lesions caused by Leishmania viannia braziliensis (Lvb). 3) To evaluate the efficacy and safety of the combination of interferon gamma and current standard therapy in the treatment of lepromatous leprosy. 4) To correlate changes in the responses of T cells in cutaneous lesions and peripheral blood with clinical responses to selected therapies.